In at least one interview you have to say ‘that’s such a stupid question, I’m not wasting my time with that’ and hang up."

Hah! :-D Don't do that.

In fact, I have had people do basically just that to me. I had one candidate (overseas) tell me in a phone screen that my questions were "too elementary" for him, "he was a manager." (And these were "general knowledge" warmups - things every engineer should know.)

The second time he said that, I pointed out that politely that everyone goes through the same process, senior or not, that whether this was right or not, we felt that engineering management needed to know how this stuff works. (And we're talking elementary here - "how fast is sorting? what sorts of collections are there?" - and the recruiters do warn the candidates that it's a "technical interview".)

After about 35 minutes it was clear I wasn't getting anywhere, so I told him we were out of time, and asked if we had any questions. "No!" he said, then hung up with some force (BANG!)

I was unfailingly polite, even though he really was pretty rude from start to finish. "This is too elementary for me" hah!

Conversely, I had a brilliant candidate from Hungary I had a phone interview with and I asked him a hard question. "Oh, that is of course a well-known question..." he says. "So what's the answer?" [extremely correct and terse answer follows] and I thought, "Well-known to *you*!" We hired him, of course... (This joke's better if you can imagine a Hungarian accent...)